Strategic
Fire Protection in Historic Buildings

Richard Forrest

The
introduction of conventional fire doors and partitions can have
a disastrous affect on a building's character and historic interest.
Risk assessment and the development of a strategic approach to fire
safety measures can lead to more sympathetic solutions.

While
modern buildings are designed from the outset to allow the occupants
to leave quickly and easily in the event of a fire, adapting an
historic building is more difficult. Two primary factors must be
considered: the protection of persons either living, working or
visiting the premises; and the protection of the building fabric
and its contents. If the building concerned is also open to the
visiting public, the requirement for life safety measures is even
greater.

The
relative priorities for life safety and property protection will
be viewed differently by those involved in the specification or
definition of requirements. The fire authorities or the local fire
brigade will be primarily concerned with ensuring that optimum standards
are achieved for the provision of means of escape and for the inclusion
of means for fighting fire. Conservationists on the other hand are
primarily concerned with preserving the building fabric without
the intrusive effects and loss of fabric that are the inevitable
consequences of most standard fire precaution measures.

The
building owner or occupier is therefore left in somewhat of a dilemma.
What are the legal requirements? What life safety standards should
be considered for the current and future usage and occupancy? What
provisions should be made to protect the building and its contents
against the ravages of fire? What are the risks?

These
questions cannot be easily answered. The only requirement in law
concerns the provision for life safety and adequate means for escape,
not the protection of property. Furthermore, current legislation
under the Fire Precautions Act 1971 relates only to those buildings
put to a designated use and unless the building incorporates office,
shop, factory or hotel use, it is unlikely that the Act and the
associated fire certification process will apply. Guides to fire
safety standards do exist. These however are based upon prescriptive
standards that are founded on generally deemed to satisfy criteria
applied to the main factors of design for life safety, such as the
provision of exits, protected routes and maximum travel distances.
These standards have no real scientific basis, but rather have evolved
over time and are considered appropriate for most building types
and occupancy.

Fire
safety design standards advocated by the current Building Regulations
primarily apply to building work only. However they can affect existing
buildings where 'material alterations' are proposed that will effectively
downgrade existing provisions covered by the regulations, such as
means of escape, fire spread and access by the fire services. They
also apply where there is a 'material change of use' including conversions
to form an hotel, a public building or a dwelling, and the subdivision
of a building to form a flat. The Regulations are a relatively recent
development responding to modern building techniques and materials.
Older buildings may have been constructed with provision for very
different methods of transferring air, heat and light around a structure,
often in the form of ducts and shafts. With the introduction of
more modern building services, the original structure may well have
been built over or adapted, creating voids. Recent tragic history
has shown, as with the fires at Hampton Court Palace and Windsor
Palace, that such voids can contribute to the propagation and rapid
spread of fire.

Recent
years have seen rapid developments in our understanding of the nature
and science of fire. As with any other facet of building development,
the specifier no longer needs to rely solely on the prescribed standards
for design: a specific tailored solution can be derived to take
full advantage of existing features.

Fire
precaution issues can be broadly broken down into two very specific
categories: 'passive' protection measures which rely on physical
barriers to restrict the development or spread of fire; and 'active'
fire protection measures including, for example, fire detector and
extinguisher systems.

PASSIVE
VERSUS ACTIVE MEASURES

Current
prescriptive fire safety standards rely very heavily on passive
protection, usually involving the enclosure of staircases and corridors
leading to final escape points and the provision of fire doors across
passageways. In addition to the intrusion that the additional doors
and partitions can cause in an historic interior, upgrading original
historic features such as doors, walls, floors and ceilings to standards
of fire resistance intended for more modern buildings is less than
ideal. The usual requirement is to ensure that all elements of a
defined fire compartment can resist the passage of fire and smoke
for a minimum period of thirty minutes. If the main elements of
the construction are masonry or similar then this standard can be
achieved relatively easily, with only nominal enhancement to breaches
in their integrity caused by pipe runs or cracks for example. However,
the main weak spots are the door openings: original doors are rarely
able to satisfy the half-hour requirement. In some cases it may
be possible to upgrade their resistance using linings and seals
with limited affect on their character and interest, but this may
not be acceptable where particularly fine work is concerned; in
other cases there may be no alternative to their complete replacement
if a passive approach to fire protection is to be employed.

Active
fire protection measures provide the fire engineer with the potential
to offset some of the more onerous passive measures by trading off
certain elements of the design process.

RISK
ASSESSMENTS AND TRADE-OFFS

The
key to a successful solution is the risk assessment, which is carried
out as part of a comprehensive fire safety review of the building,
to identify the degree of risk to both life and property. The assessment
also needs to consider any occupier requirements that may have an
effect on fire strategy. For example, where a stately home or a
museum is concerned the need to salvage artefacts could well represent
an important factor in the final definition of the fire plan for
the premises. Having identified and quantified fire risk, the basis
of fire safety design must be defined, always taking into account
the requirement to satisfy life safety issues, and to balance property
protection issues against physical intrusion.

Recent
reports commissioned by the Government to enquire into major fires
in historic premises have placed strong emphasis on the requirement
and importance of structural compartmentation. The fire plan design
philosophy should reflect this emphasis by identifying a solution
that utilises existing building features. Any existing features
which may also be beneficial such as large room volumes and high
ceilings should also be identified and incorporated into the plan.
The risk analysis should be used to provide fire safety management
recommendations aimed to reduce the probability of the outbreak
of fire and to minimise the potential effects of fire by reducing
or managing the fire load.

The
acceptability of design solutions which make full use of the existing
fabric with the minimum alteration will ultimately depend on the
length of time taken to evacuate the building safely, under fire
conditions, and assuming worst case occupation conditions.

In
some small historic buildings which contain a staircase within one
single space, with all rooms opening directly off it, further compartmentalisation
may be unnecessary. Upgrading the doors and walls to provide half
hour fire protection can be avoided by introducing an air pressurisation
system. In the event of a fire occurring in one of the rooms, the
system is activated, rapidly pressurising the escape route and forcing
smoke to leave the building through vents introduced in the rooms.
However the system has limited application as it can only be used
where the staircase is self contained, and due to the problems associated
with accommodating the large amount of plant required.

Property
protection issues may rely on automatic fire suppression, but where
a suitable system cannot be installed perhaps due to the appearance
of sprinklers, the time interval between fire initiation and detection
becomes very important. It must be recognised that all large fires
start in a small way and if detected and subsequently tackled in
the incipient stages can be prevented from developing. Where there
is no staff in permanent, 24-hour attendance who are trained to
deal with an emergency and equipped with first aid fire fighting
facilities at the building, early detection will at least ensure
the earliest attendance by the fire brigade.

The
most effective automatic means to provide fire protection to any
premises is to introduce a fire suppression system. The major benefit
of a suppression installation is that not only does it detect a
fire, it tackles it at a very early stage. The most common form
of fire suppression system is the water sprinkler. Recent environmental
issues have restricted the use of alternatives due to effects of
certain suppression gases on the ozone layer. Water suppression
research has developed rapidly and has given rise to a selection
of sprinkler and water spray systems that can be configured to provide
ultimate protection against fire growth and spread and also against
accidental activation. It is perhaps worthwhile considering that
only the sprinkler heads in the immediate vicinity of a fire would
activate and then would apply only a fraction of the water that
an attending fire service would apply to a developing fire.

RECENT
DEVELOPMENTS IN AFD

Should
fire suppression systems be considered inappropriate, the installation
of Automatic Fire Detection (AFD) can provide the vital design definition
of time interval between fire initiation and detection. AFD systems
which are incorporated with a fire alarm system have been developed
such that a variety of options exist as to operation, appearance
and potential for concealment. Traditional yoghurt pot ionisation
point detectors are now giving away to low profile optical single
point units. These tend to be less obvious and can be coloured by
the manufacturer to match surroundings. Optical beam detectors can
be installed with effect to large ceiling areas where a proliferation
of point detectors is undesirable. The units placed with a beam
source and receiver at either end of a room potentially concealed
at high level can provide adequate protection with nominal intrusion.

Where
such detection devices are to be avoided at all costs and where
risk or the design strategy dictates a requirement for AFD, aspirating
or air sampling systems may prove a viable option that can be concealed.
An aspirating system consists of a series of small diameter flexible
pipes with holes along its length. A sampling unit, positioned remotely
draws air from the room space into the sampling unit chamber, the
unit detects the presence of smoke particles and the alarm is raised.
The pipework can be concealed behind the ceiling structure, perhaps
installed from above and only very small penetrations in the ceiling
fabric need be made at intervals to allow the air to be drawn and
sampled. This technique has been used extensively in buildings having
very fine decorations and where the requirement for AFD is proved.

In
the design and installation of AFD systems for historic and listed
buildings, the identification of the best cable routes is as important
(if not more so) as the installation of the unit itself. Where it
is not possible to use existing cableways a strategy for chasing
and concealment should be agreed, which takes into account the need
to minimise damage to fine finishes, not least because repairs by
a specialist craftsman can be expensive. An alternative is to avoid
hard wiring between units by specifying a radio linked system, in
which each unit transmits data by radio frequency to a receiver.
However, in the author's experience with such installations, the
benefits of reduced wiring can be offset by larger, more intrusive
units required to incorporate radio equipment; by the cost of maintaining
the system and replacing batteries; and by the effectiveness and
reliability of signal integrity.

In
summary, as part of the development of a fire plan strategy for
any historic or listed building, the definition of risk, occupiers'
priorities and conservation issues are paramount. The fire strategy
consists of various contributory elements including the natural
or existing building features and the degree to which more onerous
passive upgrading can be offset by the introduction of active protection
measures. The ultimate active protection measure must be the introduction
of comprehensive fire suppression. This represents the only measure
to actually tackle the growth and development of a fire. In respecting
the potential difficulty in achieving fire suppression installation,
the introduction of AFD enables full advantage to be taken in design
to meet the assessed risk and to minimise passive protection measures.
Furthermore, any alterations to the original fabric which are unavoidable
should be reversible, allowing the element affected to be returned
to its original condition. Other than shallow chasing to accommodate
wiring circuits, no structural or fabric intrusion need necessarily
be made.

Finally,
in quantifying and qualifying fire risk, the building owner should
never lose sight of the difference between risk and hazard. In other
words, if in the unlikely event the worst should happen, what would
be the consequences?

This
article is reproduced from The Building Conservation Directory, 1996

Author

RICHARD FORREST is
the Director of Engineering Services with Lawrence Webster Forrest. Lawrence
Webster Forrest are leading fire engineering consultants who specialise
in providing fire safety advice to owners and occupiers of historic and
listed buildings. He has been responsible for the design of fire strategy and fire
safety systems in buildings such as The British
Museum, The Natural History Museum and the Palace of Westminster.